Nexus RV - honest mistake or something else? (updated 1/21)

This is a data point from my experience.
My brand new Itasca was listed as 2014 on all the Winnebago sales documents but the Chevy chassis was a 2013 model due to normal production/assembly timing. When I deal with General Motors they list the VIN number as 2013. That is standard depending on when the assembly of your RV happened within the year. However both my title and my registration say 2014. You didn't say your recorded registration year.
You have signed contracts - that is ammunition against their altered copies.